Salmon and oily fish
Salmon and other oily fish are rich sources of calories and protein that can help in weight gain as well as increasing the muscle mass. A 100 grams serving of salmon provides almost 142 kcal of energy, which is quite great. Salmon also gives 6 grams of fat along with 20 grams of protein. According to a study in Korea, the consumption of fish can greatly help in improving muscle mass.